Scanning horn-reflector antenna

ABSTRACT

889,490. Aerials; radio direction-finding. WESTERN ELECTRIC CO. Inc. May 25, 1960 [May 28, 1959], No. 18454/60. Class 40(7). A directional aerial system capable of providing signals for automatic tracking comprises a waveguide horn radiator feeding a paraboloidal reflector, with an elongated body of dielectric material mounted between the two for rotation about the horn axis. As described a circular waveguide (not shown) feeds a square-section waveguide horn 10, a rotatable joint being provided. The horn 10 is directed towards a paraboloidal reflector 42 and has an aperture in its upper surface through which energy can pass. The radiofrequency stages of a transducer, which may be a receiver for radio astronomy investigation, are mounted in an enclosure 24. A disc 22 mounts the smaller end of the horn for rotation in the front wall of this enclosure and the larger end of the horn carries disc 14 supported by rollers 16 and 18 so that the horn and reflector assembly can be rotated about the horn axis by motor 36, reduction gearing 20 and belt 38 asnecessary for alignment and tracking. The aerial system is carried on a turntable 12 rotatable by motor 28 for movement in azimuth for the same purpose. To provide a conical scan for automatic tracking an elongated bi-conical body 44 of dielectric material is mounted within the horn 10 so that its axis makes an angle with the horn axis. This body is supported at its centre by an oblique conical structure 46 of material of low dielectric constant mounted for rotation in rollers 48. A motor 50 is provided to drive the support 46 and thus rotate the body 44 round the horn axis. The dielectric material used to form body 44 may be a ferrite and whilst it is not essential to use a bi-conical shape tapering is &#39;desirable to reduce reflections.

Feb. 13, 1962 R. KOMPFNER SCANNING HORN-REFLECTOR ANTENNA Filed May 28. 1959 /V VEA/TOR R. KOMM-NER iinire tates @arent apaztszi Patented Feb. 13, 1962 are 3,i2i,52d SCANNEN'G REFLECTR ANTENNA iadoif Kompfner, Middletown, NJ., assigner to Bell Telephone Laboratories, Incorporated, New York, NKY., a corporation of New Yori:

Filed May 2S, i959, Ser. No. 836,514 2 Claims. till. 343-781) ln such applications, the radiation pattern of the antenna is fixed and the antenna is physically oriented in such a way as to concentrate the radiation pattern very precisely in the direction required for transmission to or reception from the next station of the relay system. It has been found, however, that the horn-reflector antenna, in addition to its other desirable properties, is capable of operation as an extremely low-noise receiving antenna. The relative freedom from back lobes in the antenna pattern fits the antenna for use in receiving signals from sources presenting a low-noise temperature. Thus, such antennas may profitably be used in radio astronomy and similar applications. ln such use, the horn-reector antenna may be considered as a low-noise temperature source of microwave energy and is particularly suited for use in connection with maser and similar low-noise amplifiers which are practicable only when the applied signal is from a low-noise temperature source.

In radio astronomy and related applications, however, the horn-reector antenna, which heretofore has been employed primarily in fixed mounts, is called upon to track a moving object. lf such tracking is to be accomplished automatically, as is extremely desirable, a source of tracking error signal is required. While this might -be furnished by a separate system of some sort, the most attractive arrangement is that in which the radiation pattern of the antenna may be shifted slightly on a periodic basis to provide for so-called lobing of the radiation pattern. The slight difference in incoming signal, which occurs when the antenna is not directed exactly at the source thereof, provides an error voltage which may be utilized in a servo system of conventional con iguration to direct a moving signal source.

It is therefore the object of the present invention to improve the horn-reflector antenna to permit its use as a scanning or tracking antenna.

In accordance with this object, the conventional hornreflector antenna, which consists of a feed horn located at the focus of a .paraboloidal reliector, is modified by mounting a dielectric body generally on an axis intersecting the axis of the feed horn and between the feed horn and the reflector. Means are provided for rotating the dielectric body about the horn axis to produce a variable difierential delay in the microwave energy as it travels from the feed horn to the reflector. From another point of view, the dielectric body may be considered as a means for adjusting the focus of the reflector with respect to its normal position at the center of the mouth of the feed horn for reception of a wave tilted so that it would otherwise not arrive at the focus. in any event, the radiation pattern of the antenna is swept in a generally circular path providing the lobing action desired.

The above and other features of the invention will be considered in detail in the following specification taken in connection with the drawing in which:

FIG. l is a perspective view partially broken away, illustrating the general configuration of a scanning antenna according to the invention; and

FiG. 2 is a partial sectional view taken on the vertical median plane of the antenna of FIG. l.

The scanning antenna of the invention is shown in FIG. l as it may be arranged for use in radio astronomy or like applications. Here, the axis of the antenna horn is shown as horizontal rather than vertical so that the antenna pattern may be in a vertical plane and the antenna may be employed in scanning the sky or tracking objects therein. Thus, a horn-reflector antenna structure l@ of essentially the same congiration as that sho-wn in the patent referred to above is mounted with its horn axis horizontal and is supported on a rotatable platform 12. To this end, the large end of the horn-reflector assembly is mounted in a disc 14 through which it extends and this disc is supported for rotation upon rollers 16 and 18 which, in turn, are journaled in a frame 20 mounted on platform 12. The small end of the antenna is supported in a smaller disc 22. which is journaled for rotation in the front face of an equipment enclosure 24, supported upon a bracket 26, also mounted on turntable 12.

The equipment enclosure 24 is shown schematically in FiG. 1 and may include, in addition to the support for the antenna, mounting and shelter for at least the initial input stages of the radio receiver or transmitter, or both, to be used with the antenna. Such an arrangement is of particular practicability with the horn-reflector antenna since the antenna is of essentially square cross-section and may 'be fed with any desirable polarization from a circular wave guide. This permits short waveguide runs to the input stages of the receiver and only a single rotatable connection or joint is required between the antenna itself and the receiver.

A motor 28 is shown as mounted on a base 3i) upon which platform 12 is journaled and provision is made for rotating platform l2 by `avay of a pinion 32 which engages a rack 34 secured to platform 12. In addition, a second motor 36, mounted on platform 12, is arranged to rotate the antenna about its horizontal axis by means of a belt or chain drive 3S. This belt extends over disc 14 and also over a drive pulley 40 which is driven through reduction gearing by the motor. It will be recognized that through rotation of platform 12 and rotation of antenna lil about its horizontal axis, any location within a hemisphere centered at the center of platform 12 may be covered by the radiation pattern of the antenna.

Although the antenna as thus far described is of considerable advantage as a low-noise temperature antenna to be used in tracking celestial objects as in radio astronomy, the fact that some external system must be provided to permit tracking of a moving object is a shortcoming. To eliminate this difliculty, there is p-rovided, in accordance with the invention, a scanning device which is located within the antenna between the feed horn source and the reector thereof. Generally, a reector 42 is so located with respect to the source that the -focus of the reflector falls at the center of the feed horn and in the plane of the mouth thereof. For the purpose of this discussion, the antenna may be considered as comprising a feed horn located in the plane of disc 22 and a paraboloidal reflector spaced therefrom along the axis of the feed horn and connected therewith by conductive extension of the feed horn walls Iwhich form a flaring box of essentially rectangular cross-sections, this box being interrupted only at the right-hand end of its upper `surface to permit radiation of waves reflected from reflector 42.

The fixed radiation pattern normally provided by this antenna configuration is caused to sweep by the interposition of a dielectric body 44 in the path between the feed horn and the reector and by the provision of means for rotating or otherwise moving the dielectric body to introduce a varying ditferential delay in electromagnetic waves radiated from the feed horn to the reflector.

In one convenientarrangement as shown in FGS. 1 and 2, the dielectric-body has a longitudinal dimension which is large as compared to its diameter or cross section in a plane at right angles to the 'longitudinal dimensionand is mounted within the extension, of the `feed horn in such a Way that the longitudinal axis of the body intersects theI axis of the feed horn. vBecause of the presence of the dielectric, the Waves traveling from the yfeed `horn to the reecy-tor are more delayed in one portionof the wave front than in another and reach the paraboloidal reflector at different times rather than simultaneously. The net result is the same as that which wouldbe introduced if the feed-horn or the reliector were 'moved sothat thefccus ofthe reflector no longer fellA at the center ofthe feed horn,.,`lf, now, the dielectric body is caused,v to rotate or otherwise move about the longitudinal axis of the antenna, the virtual focus of the assemblage will also rnove and the radiation pattern of the antenna-wi'llbe correspondingly swept with respect to the normal pattern'thereof.

As shown in the drawing, the-dielectric body 44 convenientlyt comprisesa pair of right circular' cones or" altitudes, which are large as compared to their diameters, joinedbaseyto-base and supported-with their central axes at an anglertoithe axis of the feed horn.` To this end,

a conical structure 46, which may be made of polyfoam or other material oflowdielectric constant and has the general formy offan oblique cone, is mounted with its base at right angles `to the longitudinal axis of the antenna. The dielectriovbody 44 then is mounted with its axis coincident'with the axis Aof the supporting structure Y Vand is accordingly supported with its axis intersecting the longitudinal axis of the; antenna.V Conveniently, conical structure'46 is supported by rollers 48 which extend through the walls of the antenna shield horn and are so located that conical structure 46 and the dielectric body supported thereby may be rotated within the antenna horn to'v provide the desired scanning of the antenna pattern. 'In v'FIG.' l, an electric motor 50 is externally mounted on the top-of the antenna structure and drives ,one of rollers 48 tof'provide vthe desired rotation of dielectricvbjod'y44; V y j "While: dielectric body e4 has `been shown as being a ,double cone, it will -be recognized that a wide variety of shapes may -be .employed as required to provide a sufficient diierential delayoenergy traveling from the source `to the parab'oloidal reilector of the antenna, and further, thata wide variety of materials including both the better l `lnown dielectr-ies and such materials as-ferrites may be employed for this purpose. lt is advantageous, however, to provide a dielectric body Lift, the ends of which are tapered to reduce or eliminate reflections which might otherwise occur'by virtue of the introduction of the change in dielectricconstant of the transmission medium Within the antcn'na'horn. Obviously, it is also desirable that the dielectric body and its supporting structure be of as light a Weight as possible to reduce the vibration effects introduced by. rotating an unbalanced mass Within the antenna structure, at relatively high speeds.

What is claimed is:

1. In ascanning antenna system, a horn-reflector antenna having a waveguide feed horn and a paraboloidal reflector spaced from said feed hornialong the longitudinal axis of said feed horn and interconnected by a shield horn, and means for' varying .the radiation pattern of said antenna `cdrriprising an "elongated body of dielectric material of-rnaxirnurn crossoecti'on@ less than the, corresponding cross-section of said shield horn, means supporting said body within said shield horn including a rnember of material substantially-transparent to `radio frequency energy mounted within said shield horn vfor rota tion about the longitudinal axis of said feed horn, said member supporting said body to extend generally between said feed horn and said Vreilector with the longitudinal axis of the body intersecting that of said feed horn and means external to said shield horn for rotating said niember about its axis. v

V2. In a scanning antenna A s ys'terr'igma horn-reflector antenna having a waveguide feed-horn and a reflector spaced therefrom along the feed horn axis; and means for varying the radiation pattern of 'energy radiated from 'said reflector comprising a memberv of'low dielectric constant mounted between said feed horn and said reilector for rotation about said feed horn axis,a`dielectric body which is a solid of revolution tapered at both ends and of higher dielectric constant, the length of said body along its axis being large as compared with its maximum cross-section, said body being supported by said member with the longitudinal axis of the body intersecting the feed horn axis and means for rotating said member about said feed horn axis.

References Cited in the filelof this patent UNITED STATES PATENTS 2,774,067 Bollinger Dec.A 11, 1956 2,809,371 Carter et al. Oct. 8, 1957 2,887,684 Dexter et al. o May 19, 1959 FORElGN PATENTS 1,150,023 France ,July 29, 195'] 

